The present invention relates to the production of a pipe-shaped body comprised of a synthetic resin reinforced with fibers which is formed in a generally cylindrically hollow mold rotating about its longitudinal axis and which is customarily used as a pole for supporting an illuminating device. Such poles are produced according to a known method by a screwably twisting or winding glass or mineral fibers onto a core; however this method of production has the disadvantage that the pole has no absolutely smooth surface and therefore requires an abrading or polishing after-treatment, which considerably increases production costs. Some poles are currently available which were manufactured by a rotational process in a closed mold, but due to the centrifugal force occuring during the rotational process, the interior glass fiber reinforcement is driven outwardly so far that some of the individual glass fibers protrude through the outer surface of the pole. This condition makes the surface of the pole porous, which may cause premature corrosion. Consequently there is a need to manufacture a pole according to the basically sound centrifugal process which will have a practically completely smooth surface and thereby eliminate any finishing process and lower the production costs considerably.
A smooth surfaced pole produced according to a centrifugal process is accomplished by the present invention, which utilizes a reinforcement comprising a mat that is permeable by synthetic resins and has a shape generally conforming in length and circumference to the dimensions of the inner wall of the mold. The mat initially is wound around a reeling rod in a direction opposite to the rotational direction of the mold and is inserted together with the reeling rod into the mold. The mold is then rotated while the mat is unwound from the reeling rod, so that the mat abuts the inner wall of the mold. The bare reeling rod is then withdrawn from the mold and a synthetic resin is sprayed into the mold under high pressure through a valve disposed at one end of the mold.
Since the reinforcement is fashioned to conform to the shape of the inner wall of the mold, it forms a uniform reinforcement along the whole length of the pole to be manufactured.
The reinforcement may also include a layer or layers of glass or mineral fibers lying on the inner surface of the mat. In this case, the mat is strong enough and non-porous enough to prevent any fibers from protruding therethrough and contacting the inner wall of the mold when subjected to centrifugal force.
The reinforcement may be designed for application to only particular stress areas or may be thickened for reinforcing high stress areas.
The unwinding of the reinforement and its depositing against the inner wall of the mold is problem free so long as the rotatory direction of the mold opposes the direction of winding. The reinforcement easily unwinds from the reeling rod and covers the inner wall of the mold before the synthetic resin is fed into the rotating mold. The synthetic resin subsequently sprayed into the mold penetrates the reinforcement while the mold rotates. Such penetration is aided by centrifugal force and by the high pressure under which the resin is sprayed. The mold interior can usually be visually observed so that regions of insufficient or overabundant resin accummulation may be noticed and so that the selective application of resin may be facilitated to produce a uniform pole wall thickness. On the other hand, such visual observation also permits precise, selected differences in pole wall thickness where this feature is desired. Uniform wall thickness is best achieved when the resin is sprayed from each mold end throughout a distance equalto one-half the mold length.
The process of the present invention also contemplates fastening a band, cord or the like tightly around an end of the reinforcement when it is wound around the reeling rod and removing the band when the reinforcement is inserted into the mold. Either end of the reinforcement may be provided with the band since the mold is accessible from both ends thereof.
The present invention also relates to a pipe-shaped body, such as a pole, comprising a synthetic resin and a fibrous reinforcement. The reinforcement comprises a mat which is permeable by a synthetic resin and a layer of fibers preponderantly oriented along the longitudinal direction of the mold lying on the inner surface of the mat. The specific gravity of the mat is slightly lower than the specific gravity of the synthetic resin so that the reinforcement floats on an outer layer of resin during the centrifugal process. Thereby the finished pipe-shaped body possesses a practically completely homogeneous surface of pure synthetic resin with the reinforcement disposed inwardly from the surface. The mat prevents fibers in the fibrous layers from penetrating to the surface of the pipe-shaped body. The pipe-shaped body may be easily removed from the mold after solidifying and, due to its natural shrinking, has a smooth and pore-free surface.
In another embodiment of the present invention, the mat may be fashioned of synthetic, textile or other natural fibers such as woodpulp, paper or similar materials. A woven mat is especially preferred because such a structure possesses the needed permeability to the synthetic resin. The mat may also comprise a perforated material.
The present invention further contemplates that the reinforcement may be provided with zones of different thickness so that the overall pole wall thickness varies according to the thickness of the reinforcement.
Other features which are considered characteristic of the invention are set forth in the appended claims.
Although the invention is illustrated and described in relationship to specific embodiments, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.